JPH01291133A - Resistance bulb temperature converter - Google Patents

Abstract

PURPOSE:To eliminate a measurement error generated from an unbalance of a wiring resistance by a simple adjusting operation by constituting the title converter so that data of an error portion which has been obtained by an error portion arithmetic means is given to a temperature signal arithmetic means. CONSTITUTION:A constant-current (i) from a constant-current source 3 flows to a resistance bulb 1, and in one end of a lead wire 2, voltage signals VA-VC are generated, respectively. These voltage signals are selected successively, and converted to digital signals by an A/D converter 5 through a pre-amplifier. In this state, when there is an unbalance in wiring resistances r1-r3 of the lead wire connected to the resistance bulb 1, both ends of the resistance bulb 1 are short-circuited prior to a temperature measurement in order to derive an error portion based on the unbalance, and an error portion arithmetic means 61 is allowed to calculate an error portion based on the unbalance of the wiring resistance through an operation commanding means 61. This error portion is given to a temperature signal arithmetic means 60, in which a temperature signal is calculated by taking the error portion into consideration.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a temperature conversion device using a resistance temperature detector as a sensor for detecting temperature, and more specifically relates to a method for wiring a connection path to the resistance temperature detector. The present invention relates to a resistance thermometer temperature converter that eliminates the influence of unbalanced resistance and can always obtain a signal that accurately corresponds to the measurement temperature with high accuracy.

(Prior Art) FIG. 3 is a block diagram showing an example of a device using a conventionally known resistance temperature detector as a temperature sensor.

In the figure, 1 is a resistance temperature detector, 2 is a connection path (lead wire) to the resistance temperature detector 1, and rl and r2°r3 each represent the lead wire resistance. 3 is a constant current source that supplies a constant current i to the resistance temperature sensor 1, and 4 is a voltage V at one end of the lead wire.
A, switch to sequentially switch and take out VB, VC, 5
is an A/D converter that A/D converts the voltage signal taken out by the switch 4, and 6 is a microprocessor that inputs the digital signal from the A/D converter 5, performs predetermined calculations, and generates a temperature signal. It's something you get.

In the device configured in this way, each resistance r1, r2 . Assuming that all r3 are equal and the resistance value of the temperature sensing resistor 1 is R, the following equations hold true.

rl=r2=r3 ・・・・・・(1
)VA-VC= (R+r 1 +r 3 )・i・
・・・・・・(2) VB-VC=r3-i-”・(3)(
Equation (4) is obtained from Equations 1), (2), and (3).

VA-VC-2VB+2VC=R-1 R-i=VA-2VB VC・-・-<4) In the equation (4), the current i is a constant value, and the microprocessor 6 calculates the equation (4). By doing this, the resistance temperature detector 1
The resistance value R can be calculated, and the temperature can be determined from this value.

<Problems to be Solved by the Invention> In a device having such a configuration, each resistance rl of the lead wire
, r2. Accurate temperature measurement can only be performed when both r3 are equal, and the resistance of the lead wire (wiring resistance)
If there is an imbalance, measurement errors will occur. Therefore, in order to eliminate measurement errors when there is an imbalance in such wiring resistance, conventionally, in place of the resistance temperature detector 1, prior to temperature measurement, a resistance value corresponding to, for example, 0% of the resistance temperature detector 1 is used. A resistance element was connected and adjustments were made so that the temperature calculation result would be 0%.

Such adjustment operations require an accurate reference resistor that is compatible with various RTDs, and communication between the detection section to which the reference resistor is connected and the calculation section that performs the adjustment is required. There was a problem in that it took a lot of time to make adjustments.

The present invention was made in view of these problems, and its purpose is to realize a resistance thermometer temperature converter that can correct measurement errors caused by unbalanced wiring resistance with simple adjustment operations. There is something to do.

(Means for Solving the Problems) Fig. 1 is a block diagram showing the basic configuration of the present invention. In Fig. 0, 1 is a resistance temperature detector, and 2 is a signal path (lead line), rl, r2. In both cases, r3 indicates lead wire resistance. 3 is a constant current source that supplies a constant current i to the resistance temperature sensor 1; 4 is a switch that sequentially switches and extracts the voltages VA, VB, and VC at one end of the lead wire;
5 is an A/D converter that A/D converts the voltage signal taken out by the switch 4. 60 is a temperature signal calculating means which inputs the digital signal from the A/D converter 5 and performs a predetermined calculation to obtain a temperature signal; 61 is a temperature signal calculating means that receives a digital signal from the A/D converter 5 and obtains a temperature signal; Error calculation means inputs a signal when the reference resistance of 1 is connected and calculates an error based on the unbalance of wiring resistance, and 62 is a calculation command means for operating the error calculation means 61 according to an external command signal. .

(Function) Prior to temperature measurement, short both ends of the resistance thermometer,
The error calculating means is caused to calculate the error based on the unbalance of the wiring resistance via the calculating command means. This error is given to the temperature signal calculation means, which calculates the temperature signal taking the error into consideration.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. In FIG. 6, the same parts as in FIG. 1 are denoted by the same reference numerals.

A preamplifier 40 amplifies the voltage signal at one end of the lead wire selected by the switch 4, and its amplified output is applied to the A/D converter 5, where it is converted into a digital signal. 6 is a microprocessor to which the digital signal from the A/D converter 5 is input.

In this microprocessor 6, 71 is an arithmetic control unit (CPtJ), 72 is a ROM that stores various programs and tables for performing arithmetic operations, and 73 is a ROM that stores arithmetic formula data, various externally given data, ranges, etc. A RAM stores data related to the span, an EEPROM 74 stores various data used for calculations, data given from the outside, etc., an I10 boat 75, and a communication boat 76, which are interconnected via the bus BS. It is connected.

The CPU 71 functions as the temperature signal calculation means 60, the error calculation means 61, and the calculation command means 62 in FIG. 1 by executing a program stored in the ROM 72.

Reference numeral 8 denotes a data input means, through which data such as the type of resistance temperature detector and range are inputted and given to the microprocessor 6, which includes the microprocessor, a keyboard for inputting data, a display, a communication means, etc. It consists of

A communication cable 9 is used to connect to the microprocessor 6 via a connector 90 when inputting data.

The operation of the device configured in this way will be described next.

First, it is assumed that necessary data is stored in the RAM 73 and EEPROM 74 of the microprocessor 6 by the data input means 8.

A constant current i from a constant current source 3 flows through a pair of temperature measuring resistors 1, and voltage signals VA, VB, and VC are generated at one end of a lead wire 2, respectively. These voltage signals are sequentially selected by the switch 4 and converted into digital signals by the A/D converter 5 via the preamplifier 40.

Here, the wiring resistance r of the lead wire connected to the resistance temperature sensor 1
1. r2. If there is an imbalance in r3, for example, r
When l=r+Δr and r3=r, the above equation (2) becomes (
5) The formula is as follows.

VA-VC= (R+2 r+Δr)-i...
(5) Also, equation (3) becomes as shown in equation (6).

VB-VC=r-1=(6) From equations (5) and (6), equation (7) is obtained.

R-i = VA-2VB+VC-2Δr-i...
・(7) As is clear from the comparison of equations (4) and (7), 2Δr・
1 is an error due to imbalance in the wiring resistance of the lead wire.

In the present invention, in order to obtain this error, first, both ends of the temperature sensing resistor 1 are short-circuited.

Next, in this state, each voltage signal VA, V at one end of the lead wire
The zero-order calculation command means 62, which sequentially inputs B and VC, outputs a calculation command to the error calculation means 61, and calculates the formula (8) in order to obtain the error amount 2Δr·1. ,
Such calculation commands are based on commands from the data input means 8, for example.

2Δr −i = VA-2VB+VC (8) In other words, in equation (7), if both ends of the resistance temperature detector 1 are shorted, the term R・1 becomes 0, so according to equation (8), , the error amount 2Δr−i can be obtained. When the calculation of the error is completed, the short circuit at both ends of the resistance temperature detector 1 is removed.

The error calculated in this way is E F, P T
The temperature signal is stored in the tOM 74 and given to the temperature signal calculation means 60, and by calculating the above-mentioned equation (7) in consideration of this error, there is no error due to imbalance in the wiring resistance of the lead wires. A temperature signal can be obtained.

In addition, in the above embodiment, when calculating the error amount, both ends of the resistance temperature sensor are shorted, but instead of this, a reference resistor having a certain fixed value is connected. Good too.

(Effects of the Invention) As explained in detail above, according to the present invention, even if there is an unbalance in the value of the lead wire resistance connected to the resistance temperature sensor, the error based on this can be removed by a simple operation. This makes it possible to provide a temperature conversion device that can measure temperature with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration block diagram of the present invention, FIG. 2 is a configuration block diagram showing an embodiment of the present invention, and FIG. 3 is a configuration block diagram showing an example of a conventional device. 1...Resistance temperature detector 2...Lead wire 3...Constant current source 4...Switch 5...A/D converter 6...Microprocessor 60...Temperature signal calculation means 61 ... Error calculation means 62 ... Calculation command means 8 ... Data input means (Fig. 3)

Claims (1)

[Scope of Claims] A resistance temperature detector; a constant current source that supplies a constant current i to the resistance temperature detector; a switch that sequentially switches and extracts the voltage at one end of a lead wire connected to the resistance temperature detector; An A/D converter for A/D converting the signal taken out by this switch.
a D converter; a temperature signal calculation means for inputting a digital signal from an A/D converter and performing a predetermined calculation to obtain a temperature signal; An error calculation means that inputs a signal from one end of the lead wire when a value reference resistance is connected and calculates an error based on unbalance of wiring resistance, and operates the error calculation means according to an external command signal. Calculation command means, wherein the temperature signal calculation means is given error data obtained by the error calculation means, and calculates the temperature signal by taking this error into account. Body temperature conversion device.